Various systems have been developed in the past for the purpose of attempting to capture solar energy for use. Many conventional systems employ one or more longitudinally extending reflector troughs. These troughs may be of parabolic cross section or configuration. Solar energy is reflected from the interior concave reflective surfaces of the trough for focusing onto a linearly extending solar energy collector.
In prior art systems the desireablity of maintaining the trough in proper orientation relative to the position of the sun overhead has been recognized. Proper orientation should be maintained in accordance with the latitude location of the solar energy collection device on the earth's surface and in accordance with the azimuth position of the sun in the sky. Even more important, however, is the proper orientation of the reflector device in accordance with the relative movement of the sun from east to west with respect to the earth's surface. All conventional systems heretofore employed, however, have been significantly deficient in one or more respects. In those systems where manual orientation is suggested, the practical effect is that the reflector is seldom properly focused, since the lapse of a few moments between adjustment results in a marked decrease in effeciency of energy collection. Electro mechanical systems heretofore employed have maintained proper orientation, but only with an inordinate consumption of energy in the process. For example, one half and three quarter horsepower motors have been employed to rotate the reflector dishes or troughs of conventional systems. The amount of energy necessary to effect this rotation detracts significantly from the net energy output achieved using conventional solar collection systems of this type.
Accordingly, it is a principal object of the present invention to significantly reduce the energy consumption required to maintain proper reflector orientation. This is achieved by employing a counterweight in association with the reflector trough to allow the greatest burden of necessary energy consumption in reflector orientation to be provided by the force of gravity, which maintains the reflector system in gravitational equilibruim. In conventional solar energy concentration systems a significant amount of force is required to properly orient the reflector because the center of gravity must be raised or lowered as the sun proceeds in its apparent movement across the sky. The required energy consumption is aggravated with increased size of collector systems which are necessary in order to provide a sufficient energy output to justify the initial cost and maintenance of a solar energy collection system. By employing the counterweight in the manner described according to the present invention, however, gravitational equilibruim of the system is maintained, and only a small amount of energy is required to effect orientation of the reflector to track the sun. It is estimated by providing the tracking system of the invention to conventional solar energy absorbtion systems, an increase in energy output of 30% is practical.
A further object of the invention is to provide a means for maintaining proper orientation of the reflector by preventing wind and wind gusts from disorienting the alignment of the reflector trough. This is achieved by the use of shock absorbers connected between the reflector trough and its supports. The shock absorbers allow the trough to rotate slowly to track the sun, but prevent sudden reorientation as would otherwise result from wind gusts.
A further object of the invention is to provide a longitudinally extending reflector trough designed for alignment along a North South axis with provision for adjustment of elevation of at least one end of the trough. A support or framework is provided having upright stanchions at either end. The length of the stanchions at at least one end are adjustable so that the collection mechanism may be positioned to maximize the collection of solar energy depending upon the latitude at which the mechanism is located and the azimuth of the sun above the horizon. The lower extremities of the shock absorbers are attached to the frame and may be selectively secured to the frame at different longitudinal positions therealong. Thus, the shock absorbers are always aligned at a right angle with respect to the axis of reflector rotation, regardless of the longitudinal pitch of the reflector trough. Similarly, universal joints are used at either end of the trough to couple the trough for rotation relative to the stachions.
Another object of the invention is to provide a collector tube which maximizes the efficiency of reflected solar radiation collection and retention. This is achieved by providing coaxial tubes for the circulating fluid used to collect the reflected solar energy. Thus, the fluid may flow through the innermost tube from one end of the trough to the other, and then back around the outside of that innermost tube within a second outer coaxial tube. Alternatively, flow may proceed in the opposite direction. In both instances heat radiated from the inner tube is thereby absorbed by fluid in the outer tube. In addition, an evacuated coaxial sleeve may be provided around the outer tube. The vacuum therein reduces radiation outward from the outer tube. Preferably, the sleeve is shaped with a semi-circular configuration on its lower surface to match the parabolic configuration of the reflector trough. Reflected radiation thereby penetrates the sleeve from the trough normal to the surface of the sleeve. The top or upper surface of the sleeve, on the other hand, is flat, thereby reducing the volume of circulating fluid to increase the volumetric concentration of solar energy in the fluid. This raises the temperature of the fluid so that thermal energy may be extracted therefrom more efficiently.
A further object of the invention, especially as applied to plate collectors, is to obtain an advantage in facilitating maintenance. In conventional systems, rectangular collectors are packed side by side in a fixed rectilinear array. Consequently, a defect in an interiorally located panel is extremely difficult to reach and service. Using the tracking and orientation system of the present invention panels need merely be tilted on edge to provide a passageway for access to the interior panels.